MSA (Multiplication Stimulating Activity) is an insulin-like peptide which reacts with its own receptor and the insulin receptor. MSA is elevated in about 40% of patients with hypoglycemia and non-islet cell tumors. Patients with hemangiopericytoma have elevated circulating MSA levels. Cells from two hemangiopericytoma patients have been put into tissue culutre. Analysis of proteins from both the cells and the conditioned media suggests production of both an insulin-like growth factor and a binding protein.